ST. LOUIS — The razor-thin margin, the single-point difference came on a free throw set up by an exquisite pass by a fun-loving sophomore named Draymond Green, a play that has come to symbolize what Tom Izzo has created at Michigan State.

One pass, one shot, one final defensive stop and another line added onto Izzo’s remarkable resume.

“There’s nothing greater than going to the Final Four that I know of,” Izzo said, “except maybe winning it.”

No one knows it better than Izzo, headed to his sixth Final Four in the last 12 years after yesterday’s tenuous 70-69 victory over Tennessee in the Midwest Region final at Edward Jones Dome. A year ago, the Spartans achieved a coveted goal by getting to the Final Four in Detroit, in their home state. This time around Michigan State (28-8) on Saturday confronts a reversal of fortune, facing mid-major upstart Butler in a national semifinal game — and battle of five-seeds — in Indianapolis, six miles from Butler’s campus.

Under Izzo, Michigan State is a stunning 9-1 in its last 10 NCAA tournament games and securing this one took some serious maneuvering. The difference on the scoreboard was Raymar Morgan’s free throw with 1.8 seconds remaining in a game in which both sides had the same number of baskets (24) and rebounds (27). There wasn’t much difference, other than the Spartans somehow find a way.

The Volunteers (28-9), in the Elite Eight for the first time in school history, came up painfully short. Durrell Summers (21 points on 8 of 10 shooting to earn the regional’s Most Outstanding Player award), drained a 3-pointer for Michigan State to make it 69-66, but Brian Williams of The Bronx slammed home an offensive rebound to pull Tennessee within 69-68.

With 28.9 seconds left sophomore guard Korie Lucious was fouled by Melvin Goins out near half-court. Lucious, forced into the starting lineup after senior point guard Kalin Lucas in the second round went down to a torn Achilles’ tendon, missed the front end of a 1-and-1 and the Volunteers had another chance. Green fouled Scottie Hopson on a jumper, putting Hopson on the line with 11.2 seconds remaining.

“I kind of told him I need one of these to come off, or if you can give me both,” Lucious said to Hopson.

Only a 60 percent foul shooter, Hopson made the first and missed the second for a 69-69 tie.

Here’s where the Spartans stayed cool amid the heat of the moment. During a timeout, Izzo was about to design the crucial play when the charismatic Green chimed in.

“I told coach, ‘Isolate me on top, get me the ball, I want to break him down,’ ” Green said. “The play he drew it up, I knew I wasn’t going to run it.”

Lucious, wearing down in his 35th minute, got the ball to Green on the high post.

“I was ready to drive to the basket or take the shot,” Green said. “But I saw Ray wide open. It was a heads-up play by Raymar to wave his hands because if he didn’t wave his hands, I probably would have shot the ball.”

Green threaded a perfect wrap-around pass inside to Morgan, shockingly free. All J.P. Prince could do was hack away as the whistle blew with 1.8 seconds to go.

“At the end of the game you let the players win the game,” lamented Prince, who two nights earlier blocked a last-second shot by Ohio State’s Evan Turner. “It’s unfortunate he called it. It’s a tough way to go out.”

Pearl had no complaint.

“We didn’t get matched up properly and they got the ball too close to the basket,” he said. “They got too good a look and a foul was called.”

Morgan made the first free throw and then was instructed to intentionally miss the second. Williams grabbed the rebound and the Vols immediately called time with only 1.6 seconds to work with. Prince’s half-court heave fell short at the buzzer, leaving the Spartans with a date with Butler.